Type 1 diabetes mellitus (T1DM) results from permanent loss of insulin secretion. Optimal treatment requires significant patient effort including multiple insulin injections every day or subcutaneous insulin infusion through a pump to maintain near-normal blood glucose. Inadequate treatment of T1DM results in hyperglycemia and eventual microvascular damage in vital organs such as the eyes and kidneys. Adolescents with T1DM are generally in worse metabolic control than their adult counterparts. This is most likely due to lack of adherence to prescribed insulin therapy, which manifests as missed mealtime boluses and snacking without insulin. Interventions to reduce the frequency of adolescent insulin omissions have largely been unsuccessful, and many believe that adolescent poor glycemic control in T1DM can only be addressed with an artificial pancreas. The University of Virginia (UVa) has pioneered the field of artificial pancreas research in recent years, leading to the development of a model predictive control algorithm that significantly improved overnight blood glucose control in adults with T1DM in a 2008 study. A similar algorithm is FDA approved and currently being used in a clinical trial to reduce hypoglycemic events and hyperglycemia in adolescents with T1DM at UVa. This control- to-range algorithm is "supervisory," meaning that it is only active if blood glucose levels are predicted to exceed a safe range (70-180 mg/dL). The safety inherent in the control-to-range algorithm makes it an attractive solution for the pediatric population. However, before this algorithm can be put into widespread use, more testing is needed to evaluate it under real-life challenges such as eating without insulin. Snacking without an insulin bolus is a common occurrence that needs to be addressed in the adolescent T1DM population, and provides an expected and valid test of the control-to-range algorithm. By addressing these real life challenges to teens with type 1 diabetes, this research could lead to improvements in ever-evasive adolescent glycemic control. Specific Aim 1: Test the hypothesis that a control-to-range module can reduce hyperglycemia in adolescents following omission of insulin for a snack. Specific Aim 2: Evaluate the safety of a control-to-range module in avoiding hypoglycemia from boluses to correct hyperglycemia in adolescents with type 1 diabetes. PUBLIC HEALTH RELEVANCE: Adolescents with type 1 diabetes historically maintain worse control of their disease compared with other populations such as children and adults. This is usually from lack of adherence to treatment plans and missing insulin injections. An artificial pancreas, such as the one developed by our research group, could be the key to improving diabetes control in adolescents.